Phoenix Final Descent Trajectory Options

[ElkGroveDan]

Richard was such a great narrator. Count me as one vote to have him call out MSL when the time comes, even if he's not part of that team. There's a certain amount of excitement in his voice, but its subtle enough to not be a distraction. That 9 minutes was one of the most exciting and enjoyable as any space related live event in my 47 years of following these events.

EDIT: admittedly I guess I didn't follow my first one too closely, Explorer 11 -- being an infant at the time.

[Guest_Oersted_*]

As I told Doug, I wish the rules allowed people like me to borrow your skills to help us. I don't know how many times I wish I could post something here and have some of you do some engineering / rendering for me! (the price is right and you all have the"chops" to do this)

Of course Rob Manning wouldn't be allowed to do that, but I don't see a problem with an anonymous UMSF member going by the user name MarsEngineer, whoever he would be, posting little tidbits from time to time...

[nprev]

That 9 minutes was one of the most exciting and enjoyable as any space related live event in my 47 years of following these events.

I gotta chime in & totally agree with this statement, Dan...it was really terrific, will never forget it!

[mcaplinger]

As I told Doug, I wish the rules allowed people like me to borrow your skills to help us...

Of course, one might wonder why JPL, which as far as I know has a team of several people to do nothing but "visualization", would need to do that in the first place.

[elakdawalla]

Geez, Mike, can't you let a guy throw a bone to his fans?

--Emily

[Guest_Oersted_*]

Maybe kwan will get a job offer from Maas Digital soon?

[djellison]

Of course, one might wonder why JPL, which as far as I know has a team of several people to do nothing but "visualization", would need to do that in the first place.

Come on Mike - that's not exactly fair. Sometimes, even though the talent is there, the time or money to do something isn't. Surely you more than most here, should understand that.

DOug

[OWW]

Correct me if I'm wrong, but did the lander legs deploy twice in the animation? The first time just after heatshield separation at 4:12? The second time at 5:36.

[dmuller]

Well I think in "kwan vs JPL Visualization" (sorry for putting it that way) we are talking about two different things.

Kwan's animation is amazing because it is scientifically and engineering-wise "correct", which is of great excitement for those interested in the science and engineering of it all (i.e. the majority on this forum).

The JPL Visualization's task, I can imagine, is to sell "space" and "spaceflight" to the masses (and hence guarantee funding etc). So that stuff has to look good. I somehow doubt that the big masses do get any excitement out of the big wobbles prior to parachute deploy, the resonances of leg deploy, the steadiness at constant velocity

[Skyrunner]

Of course Rob Manning wouldn't be allowed to do that, but I don't see a problem with an anonymous UMSF member going by the user name MarsEngineer, whoever he would be, posting little tidbits from time to time...

It would be neat if JPL could build a piece of SW in the lines of Meastro that let us do al kinds of imaging stuff. Give us a course we have to complete. Ensure the program documents all steps the user takes to alter the image, panorama or anaglyph. Unfortunately NASA would need another way to protect it's data. Now their researchers can just keep the calibration data to ensure they can work towards the results they have already invested years in. I guess it would not be very doable to let us all sign an NDA kind of document. It would be cool if we enthusiasts could all help with the 'simple' tasks (as far as simple tasks exist...let me rephrase that to relatively simple, repetitive tasks) to lighten the burden on the team but giving them al the credit were it is due (of course UMSF would be noticed in the image credits ).

Just daydreaming

[kwan3217]

Correct me if I'm wrong, but did the lander legs deploy twice in the animation? The first time just after heatshield separation at 4:12? The second time at 5:36.

In my animation, the legs deploy at 4:12-4:13 and stay down. The geometry is poor and most of the event is hidden by the backshell. However, the commentary doesn't mention the legs until 5:35. Either the telemetry for the legs took that long to come down (possible and understandable, mechanical one-time telemetry might run at a slow rate) or the commentator didn't notice until then (Also understandable, he seemed to be focused on the radar telemetry)

As for competing with JPL, nothing I have done is hard. It's about 250 lines of animation script, which is basically just read the table, orient the model, draw the frame, repeated 13152 times. I'd be precisely nowhere without the hard work of the guys at JPL who figured out the stuff that's in the tables (Not to mention getting a real spacecraft to Mars in the first place).

I'm also nowhere near Dan Maas and crew. I make animations to see what things "really look like" and I've been disappointed with a lot of my work because to be honest, space events are hard to film. The lighting is never right. It's hard to see critical events. Space is slow. As mentioned above, two minutes hanging on a parachute? From a fixed view point? Whoopee. Maas and crew, and the vis guys at JPL have the cinematography skills and tools to make these events look good and exciting. I am still practicing. I aspire to Maas-like quality, but I'm still a little ways away.

[gallen_53]

Version 1B

What I found particularly interesting in this animation was seeing the dynamic instability growing in the aeroshell's angle-of-attack just before parachute deployment. This phenomena was first seen with the Viking aeroshells and would have caused the aeroshells to tumble if Viking didn't have a reaction control system. The dynamic instability is triggered by shockwave separation due to reducing Mach Number but driven by vortices in the aeroshell's wake and real gas effects (very difficult to model).

[nprev]

THAT is an interesting tidbit! So parachute deployment is as much about keeping the vehicle stable at low Mach as it is about deceleration...great dual-application solution.

Has anyone ever considered using a ribbon chute for stabilization & holding off on a main conventional chute for later? Seems like getting a single chute to work properly in supersonic conditions is a real challenge ("squidding"), don't know if its behavior is easier to simulate or predict at lower speeds, nor if it would provide enough deceleration if deployment were deferred.

[gallen_53]

THAT is an interesting tidbit! So parachute deployment is as much about keeping the vehicle stable at low Mach as it is about deceleration...great dual-application solution.

Yes, the 70 deg. sphere-cone becomes dynamically unstable at around Mach = 1.8 . A 45 deg. sphere-cone such as used with Pioneer Venus or the Galileo Probe can be aerodynamically stable all the way to the ground provided the center-of-gravity is correctly located. However a 45 deg. sphere-cone has significantly less drag that the 70 deg. sphere-cone. Because the Martian atmosphere is so thin, you want the vehicle to decelerate as rapidly as possible (maximum bluntness is highly desireable).

Has anyone ever considered using a ribbon chute for stabilization & holding off on a main conventional chute for later? Seems like getting a single chute to work properly in supersonic conditions is a real challenge ("squidding"), don't know if its behavior is easier to simulate or predict at lower speeds, nor if it would provide enough deceleration if deployment were deferred.

Mars landers use a disk-gap-band parachute because that type parachute can safely deploy at supersonic speed. One would prefer to deploy the parachute subsonically but that's not really an option on Mars due to the thin atmosphere.

Designing parachutes is a black art. Correctly simulating a parachute with a computer model is hard to do. Also squidding can happen at subsonic speeds. The early MER parachute prototypes squidded in the NASA Ames 40 x 80 wind tunnel at subsonic speeds.

[Guest_Oersted_*]

The JPL Visualization's task, I can imagine, is to sell "space" and "spaceflight" to the masses (and hence guarantee funding etc). So that stuff has to look good. I somehow doubt that the big masses do get any excitement out of the big wobbles prior to parachute deploy, the resonances of leg deploy, the steadiness at constant velocity

No, they also do the visualization of actual data that comes down. See for example the MER airbag bounce movie.